1. Technical Field
Several aspects of the present invention relate to a technology for controlling behaviors of various driven elements such as OLED (organic light emitting diode) elements, liquid crystal elements, electrophoresis elements, electrochromic elements, electron emission elements, resistive elements, and sensor elements.
2. Related Art
An electronic device that uses a transistor (hereinafter referred to as a “driving transistor”) in order to generate a voltage or current for driving a driven element of the above type has been proposed. For example, in a light emitter that employs OLED elements as driven elements, the values of currents supplied to the OLED elements are controlled by driving transistors provided correspondingly to the OLED elements. This configuration of the light emitter has a problem in that an error in driving transistor characteristic (particularly a threshold value) causes a variation in driving state (such as a grayscale level or brightness) of each driven element. To solve the above problem, JP-A-2004-245937 discloses a configuration for compensating an error in driving transistor threshold value.
FIG. 17 is a circuit diagram showing the configuration disclosed in JP-A-2004-245937. In this configuration, first, a transistor TrA is used to connect a driving transistor Tdr to operate as a diode. This sets a gate of the driving transistor Tdr to have a potential (represented by “Vdd−Vth”) based on threshold value Vth. The potential is held by a capacitive element C1. Second, by electrically connecting a data line L and an electrode “a” of a capacitive element C2 through a transistor TrB, a potential (gate potential of the driving transistor Tdr) at the electrode “a” is changed depending on potential Vdata of the data line L. Accordingly, the gate potential of the driving transistor Tdr changes by a level based on a change in potential of the electrode “a”, and current Iel (independent from threshold voltage Vth) based on the changed potential is supplied to drive an element E. In order to realize high definition of the driven elements and screen enlargement, it is necessary to set the gate of the driving transistor Tdr to have the potential (Vdd−Vth) based on threshold voltage Vth, and it is also necessary to increase a time for changing the set potential depending on potential Vdata.